Abstract
Cellulosimicrobium cellulans (also known with the synonyms Cellulomonas cellulans, Oerskovia xanthineolytica, and Arthrobacter luteus) is an actinomycete that excretes yeast cell wall lytic enzyme complexes containing endo-β-1,3-glucanases [EC 3.2.1.39 and 3.2.1.6] as key constituents. Three genes encoding endo-β-1,3-glucanases from two C. cellulans strains have been cloned and characterised over the past years. The βglII and βglIIA genes from strain DSM 10297 (also known as O. xanthineolytica LL G109) encoded proteins of 40.8 and 28.6 kDa, respectively, whereas the β-1,3-glucanase gene from strain ATCC 21606 (also known as A. luteus 73–14) encoded a 54.5 kDa protein. Alignment of their deduced amino acid sequences reveal that βglII and βglIIA have catalytic domains assigned to family 16 of glycosyl hydrolases, whereas the catalytic domain from the 54.5 kDa glucanase belongs to family 64. Notably, both βglII and the 54.5 kDa β-1,3-glucanase are multidomain proteins, having a lectin-like C-terminal domain that has been assigned to family 13 of carbohydrate binding modules, and that confers to β-1,3-glucanases the ability to lyse viable yeast cells. Furthermore, βglII may also undergo posttranslational proteolytic processing of its C-terminal domain, resulting in a truncated enzyme retaining its glucanase activity but with very low yeast-lytic activity. In this review, the diversity in terms of structural and functional characteristics of the C. cellulans β-1,3-glucanases has been compiled and compared.
Highlights
Several bacteria have been reported to be able to lyse and grow on viable yeast and fungal cells by producing a variety of cell-wall degrading enzymes such as endo-β-1,3-glucanases, proteases, β-1,6-glucanases, mannanases, and chitinases
The structural complexity of the yeast cell wall, which is mainly composed of complex polymers of β-1,3and β-1,6-glucans, mannoproteins, and smaller amounts of chitin [1,2], implies that the synergistic action of these enzymes is necessary to hydrolyse its components into assimilable substrates
Strain ATCC21606 is known as A. luteus 73/14 Strain DSM10297 is known as O. xanthineolytica LL-G109 a Assuming a molecular weight of 4000 for laminarin b Using S. cerevisiae cells as substrate c at 30°C d at 37°C e estimated from SDS-PAGE analysis m needs 2-mercaptoethanol r recombinant form t truncated form
Summary
Availability of recombinant C. cellulans β-1,3-glucanases has opened the door to comprehensive characterisation (and future engineering) of these biotechnologically important enzymes, which is key for the development of new/potential applications or the optimisation the existing ones. A better understanding of the basis of the substrate specificity and interactions with the yeast cell wall components still awaits a detailed comparison of the three-dimensional structures of these enzymes and http://www.microbialcellfactories.com/content/5/1/10 systematic experimental verifications of the derived conclusions by protein engineering
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